OCR Text |
Show remain suspended in the gas burn totally in the gas phase. Their mineral matter content is either entrained as small particles out of cyclone or it is transported to the walls by diffusion through the boundary layer, basically describable via a Reynolds analogy model. The histograms of the particle size distribution of both coal types fed into the cyclone are shown in Figure 3 and the proximate analyses of the coals are shown in Table 1. A detailed summary of performance results is given in Table 2.(2-4) 3.0 ANALYSIS The general flow pattern of gas in cyclone burners is generally recog- (5) nized to be complex/ The gas velocity consists of three components, (i) tangential, (ii) axial and (iii) radial, and they are in general a function of radius ana axial location in the burner. The tangential component is responsible for imparting the radial momentum to the particles which is either aided or opposea by tne radial component of gas velocity depending upon the direction of radial flow of gas. Thus the time for particles to reach the wall is dependent upon the , .tribution of radial and tangential gas velocity components. The mean axial component determines the residence time of gas in the burner. With this fundamental description of the flow pattern within the cyclone, one can arrive at a set of equations for momentum balance of the particles, in all three directions, based upon assumptions of the flow field structure. 3.1 ASSUMPTIONS In order to obtain controlling groups of variables which determine the particle time to reach the wall, the following assumptions are made to simplify the analysis: (i) Gas velocity field assumed independent of particle momentum transport or momentum defect. (ii) The coal particles when injected travel with the same local tangential velocity as the gas. No injection penetration or residual velocity is considered. -5- ^7AVCO EVERETT |